内蒙古商都大石沟花岗岩体锆石SHRIMPU-Pb年龄及其意义

SHRIMP U-Pb dating of Dashigou biotite-K-felspar granites in Shangdu,Inner Mongolia,and its significance.

内蒙古商都县大石沟黑云母钾长花岗岩主要由钾长石(40～60%)、更长石(10～15%)、石英(25～32%)及黑云母(5～7%)组成。主元素SiO_2含量68.25%～69.64%,K_2O含量5.03%～8.03%,K_2O>Na_2O;A/CNK为0.77～1.1,稀土元素分馏较强,REE配分型式具中等铕负异常,岩石地球化学特征与碰撞花岗岩类似;本文对大石沟黑云母钾长花岗岩进行高精度锆石SHRIMP U-Pb定年研究。其形成时间为342±5Ma,可能代表华北板块与西伯利亚板块碰撞阶段的岩浆热事件。区域最新研究资料表明,侵入图林凯蛇绿岩带的埃达克岩的年龄为467～429Ma,代表洋壳俯冲的消减时间;390～310Ma花岗岩侵位的SHRIMP U-Pb锆石年龄以及383Ma蓝片岩Ar-Ar年龄代表华北板块与西伯利亚板块的碰撞事件;390～342Ma和324～310Ma花岗岩可能代表碰撞阶段两期岩浆热事件产物。

The Dashigou biotite K-felspar granites consists mainly of orthoclase（40% - 60% ）, oligoclase（ 10%-15% ）, quartz （25%-30% ）and biotite（5%- 7% ）in the Shangdu county of Inner Mongolia. The biotite K-felspar granites are characterized with SiO2 （ 68.25%- 69.64% ）, K2O （5.03%-8.03% ） contents, K2O 〉 Na2O and A/CNK = 0.77 - 1.1, as will as fractionated REE patterns with middle negative Eu anomalies. The geochemical characteristics are similar to collision granites. Using High-precision SHRIMP U-Pb zircon dating method, We determine the Dashigou high-K granitoids were formed at 342±5Ma, the results indicate that the collision event of China plate with Xiboliya. took place in the Early Carboniferous epoch. Integrated with that the adakites, indicating the oceanic subduction event displaced at 467 -429Ma from Tulinkai ophiolite zone. The 383Ma of glaucophane-schist Ar-Ar age from Sunitezuoqi region and 390Ma-310Ma SHRIMP U-Pb age of granites from the northern margin of the North China reflects that collision events between the North China and Xiberia Plates; 390Ma-342Ma and 324Ma -310Ma of SHRIMP U-Pb zircon age of granitoids indicates two stage magmatism of the collision orogenic processes.